Optical computer element

ABSTRACT

The invention relates to an optical computing element for use in an optical computer utilizing computing light rays having a plurality of wavelength components. The optical computing element comprises a photo-chemical hole burning element which functions as a wavelength selecting filter of the computing light rays. Therefore, the optical computer using the photo-chemical hole burning element of the invention can perform arithmetic operations by taking advantage of differences in optical wavelength. The computer can efficiently perform bulky arithmetic processing, and can also speedily perform arithmetic operations through simultaneous parallel processing for information.

RELATED APPLICATION

This application is a division of U.S. application Ser. No. 07/571,761filed on Aug. 23, 1990, now abandoned which in turn is acontinuation-in-part of U.S. application Ser. No. 07/312,073 filed onFeb. 16, 1989, now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical computing element for use in anoptical computer which performs optical parallel operation of themultiplex wavelength type.

2. Description of the Prior Art

FIG. 1 is a fundamental schematic diagram illustrating a conventionaloptical parallel computer as shown, for example, in Oyo Buturi, vol. 54,No. 10 (1985), pp. 1019-1030. The FIG. 1 optical computer is a computerof the so called non von Neumann type in which a central processing unit16 (hereinafter referred to as CPU) and a memory 17 are interconnectedin parallel by a plurality of signal lines through an opticalinterconnection 8 capable of changing a coupling area. Input ofinformation to the CPU 16 and output from the CPU 16 are channeledthrough an input output part 18.

Since the CPU 16 and the memory 17 are interconnected in parallel asabove mentioned, programs, data items, and the like are written into andread from the memory 17 in parallel relation through individual signallines.

With such conventional computer of the non von Neumann type, as abovementioned, however, the difficulty is that although there are amultiplicity of signal lines arranged in parallel, one signal line candeal with one signal only, which fact makes it impracticable to performbulky operation in an efficient manner.

In an attempt to overcome this difficulty there has been proposed anoptical computer in which light rays having a plurality of wavelengthsare used as computing light rays to enable arithmetic operations to beexecuted in optical wavelength orders. However, there has been nocorresponding development of an element which could control only aparticular wavelength component of such computing light rays having aplurality of wavelengths.

SUMMARY OF THE INVENTION

This invention is directed to solving the foregoing problems with theprior art, and the optical computing element of the invention for use inan optical computer capable of performing wavelength multiplexed opticalparallel operations is a photo chemical hole burning element(hereinafter referred to as PHB) useful as a wavelength selecting filterof computing light rays having a plurality of wavelength components. Theelement in accordance with the invention can be employed in opticalcomputers for various purposes, such as input light wavelengthselection, output light wavelength selection, threshold value processingin an operation gate array, optical memory, and optical interconnection.

It is a first object of the invention to provide an optical computingelement for use in an optical computer which enables arithmeticprocessing utilizing differences in optical wavelength.

It is a second object of the invention to provide an optical computingelement for use in an optical computer which enables bulky arithmeticprocessing.

It is a third object of the invention to provide an optical computingelement which enables selection of light rays having a necessarywavelength for arithmetic processing which it is used as an element forinput light wavelength selection.

It is a fourth object of the invention to provide an optical computingelement which enables selection of light rays having a necessarywavelength after arithmetic processing when it is used as an element foroutput light wavelength selection.

It is a fifth object of the invention to provide an optical computingelement which enables performance of gate functions in wavelength orderswhen it is used as a gate array for a sequential logic system.

It is a sixth object of the invention to provide an optical computingelement which enables threshold processing to be performed in wavelengthorders when it is used as a nonlinear threshold element.

It is a seventh object of the invention to provide an optical computingelement which enables information to be recorded in multiplexwavelengths when the element is used as an optical memory element.

It is an eighth object of the invention to provide an optical computingelement which enables different optical interconnections to be formedfor individual wavelengths when the element is used as an opticalinterconnection element.

The above and further objects and features of the invention will morefully be apparent from the following detailed description withaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a fundamental configuration of anoptical parallel computer;

FIG. 2 is a schematic diagram illustrating the concept of wavelengthselection with an optical computing element according to the invention;

FIG. 3 is a block diagram showing a fundamental arithmetic unit;

FIGS. 4(a)-4(c) are schematic diagrams showing, by way of example, formsof optical interconnection between arithmetic units;

FIG. 5 is a schematic diagram showing an embodiment in which the elementof the invention is used as an input element, particularly illustratinga photo-chemical hole burning element having pits for selecting outputwavelengths;

FIG. 5a illustrates a spectrum of a light beam applied to the pits inFIG. 5;

FIG. 6 is a schematic diagram showing an embodiment in which the elementof the invention is used as an output element, particularly illustratinga photo-chemical hole burning element having pits for selecting outputwavelengths;

FIG. 6a illustrates a spectrum of a light beam incident on the pits ifFIG. 6;

FIG. 7 is a schematic diagram showing an embodiment in which the elementof the invention is used as a gate array;

FIGS. 7a-7d illustrate a spectrum of a light beam during respectiveprocessing stages shown therein;

FIG. 8 is a schematic diagram showing an embodiment in which the elementof the invention is used as a nonlinear threshold element;

FIG. 8a illustrates the relation between the incident intensity and theoutgoing intensity of the light beam having a given wavelength incidenton one of the pits in FIG. 8;

FIG. 9 is a schematic diagram showing an embodiment in which the elementof the invention is used as a memory/delay element;

FIGS. 9a-9c illustrate a spectrum of a light beam having a particularbandwith emitted from the respective pits;

FIG. 10 is a schematic diagram showing an embodiment in which theelement of the invention is used as an optical interconnection element;

FIG. 11 is a diagram illustrating further details relating to thewavelength selection with an optical computing element according to theinvention;

FIG. 12 illustrates more of a system arrangement in which multiple pitsare each selectively controllable from the control unit; and

FIGS. 13(a), 13(b), 13(c) and 13(d) illustrate different opticalabsorption rates of signals depending upon the electric field applied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the invention will now be described in detail.

Firstly, the concept of wavelength selection by means of the computingelement in accordance with the invention will be explained. FIG. 2 is aschematic diagram illustrating the concept. In FIG. 2, numeral 1designates a pit (an area having a certain expanse as one informationunit on which a wavelength multiplexed light beam is incident) within aPHB medium. The pit 1 is electrically or optically controlled by acontrol unit 2 with respect to its PHB characteristics (wavelengthselectivity).

Next, the manner of operation will be explained.

Light rays having multiplexed wavelengths are incident on individualpits 1 in the PHB medium. The incident light in this case consists ofm-number of light rays of different wavelengths, λ₁ - λ_(m), including dnumber (d≦m) of data light rays and (m - d) number computing or controllight rays. The PHB characteristics of each individual pit arecontrolled by the control unit 2 or control light rays so that lightrays of particular wavelengths λ_(i), λ_(j) (1≦i, j≦m) only are allowedto transmit.

Therefore, the wavelength selectivity of each pit can be controlled asdesired, it being thus possible to deal with various pieces ofinformation by taking advantage of the differences in wavelength. Inother words, units of information can be dealt with in wavelengthorders. This makes it possible to arrange signal lines in parallel sothat the signal lines can individually permit wavelength-multiplexing,which means increased capacity of information processing.

FIG. 3 is a schematic diagram showing a fundamental arrangement of anoptical apparatus to which the above described concept is applied. InFIG. 3, numeral 7 designates a hybrid processing unit (hereinafterreferred to as HPU) having en bloc all functions of the CPU 16, memory17, and input/output part 18 shown in FIG. 1, and numeral 8 designatesabove mentioned coupling-area variable optical interconnection, the HPU7 and optical interconnection 8 constituting an arithmetic unit 4. Onthe optical input side of the arithmetic unit 4 there is disposed alight emitting part 9 emitting wavelength multiplexed light rays; andthere is disposed a beam splitter 12 between the light emitting part 9and the HPU 7. A light receptor part 10 is disposed on the opticaloutput side of the arithmetic unit 4, there being provided a beamsplitter 13 between the light receptor part 10 and the opticalinterconnection 8. There are provided mirrors 15 and 14 opticallysuitably positioned relative to the beam splitters 12 and 13respectively in order to cause a light beam from the arithmetic unit 4to be incident on the arithmetic unit 4 again. The arithmetic unit 4,beam splitter 13, mirrors 14, 15 and beam splitter 12 are arranged toform one optical path. Shown by 11 is a control part which controlsthese optical members altogether.

The manner of operation will now be explained.

Wavelength-multiplexed light rays emitted from the light emitting part 9become incident on the arithmetic unit 4 via the beam splitter 12. Inthe arithmetic unit 4, one or more kinds of processing of various kindsof processing, such as input light wavelength selection, output lightwavelength selection, arithmetic gate array threshold processing, andwavelength selection for the optical interconnection, are carried out.After the processing, a part of the light beam emitted from thearithmetic unit 4 is inputted directly to the light receptor part 10,and the rest of the light beam is caused to become incident on thearithmetic unit 4 again through the beam splitter 13, mirror 14, mirror15, and beam splitter 12, for next processing.

In FIG. 3, only an optical axis is shown with respect to signal lines,but it is to be understood that the light transmission has a spaciousexpanse and that individual signal lines are so arranged as to permitwavelength multiplexing.

FIG. 4 is a schematic diagram showing, by way of example, forms ofoptical interconnection In the drawing, 7a, 7b designates HPU, with anoptical connection 8 disposed between the first stage HPU 7a and thesecond stage HPU 7b. FIG. 4(a) shows an instance in which signals aretransmitted from the first stage pits 1 to the second stage pits 1, inone to one relation. In this instance, arithmetic operations can becarried out in simultaneous parallel relation without correlation of thefirst and second stage pits. In FIG. 4(b). there is shown an instance inwhich optical information from one first stage pit 1 is transmitted toall second stage pits, in which case holographic processing, such asassociative memory, can be carried out. FIG. 4(c) shows a case in whicheach pit has a variable coupling area. In this instance, flexible dataprocessing can be performed. As above described, according to thisembodiment, parallel arithmetic operations in which the coupling areasare variable, in addition, an information from one or more first stagepits in wavelength orders is effectively coupled in one second stage pitor between a plurality of second stage pits, whereby processingoperations, such as image processing, numeric value computation, patternmatching, associative memory, and deduction machine, can be efficientlycarried out.

Next, embodiments in which the optical computing element of theinformation (hereinafter referred to as the element of the invention) isemployed will be described in detail.

FIG. 5 is a schematic diagram showing an embodiment in which the elementof the invention is employed as an input light wavelength selectingelement. In the drawing, 3 designates a PHB medium, and 1a, 1b designatepits. In this embodiment, each pit 1a, 1b independently acts as awavelength filter, which controls input light rays having n number ofwavelengths, with such wavelength spectra as shown in FIG. 5(a). In thepit 1a, only a light ray having a wavelength λ_(i1) is allowed totransmit, whereas in the pit 1b, only light rays having wavelengthsλ_(i2) and λ_(i3) are allowed to transmit. In this way, spectralpatterns corresponding to information items to be dealt with can beobtained as desired.

FIG. 6 is a schematic diagram showing an embodiment in which the elementof the invention is used as an output light wavelength selectingelement, the arrangement of which is same as that of the previousembodiment in which the element is used as an input light wavelengthselecting element. Whereas, in the previous case for input lightwavelength selection, light rays of such wavelength as is necessary forarithmetic operation in general are selected, in the case of outputlight wavelength selection, light rays of such wavelength as isnecessary as a result of arithmetic operation are selected.

FIG. 7 is a schematic diagram showing an embodiment in which the elementof the invention is employed as a gate array for a sequential logicsystem. In the drawings, 1a, 1b and 1c designate pits, 3 designates aPHB medium, and 8 designates an optical interconnection. In the gatearray of this embodiment, signal lines are individually arranged topermit wavelength multiplexing so that in the pits connected in thesequence of a series of arithmetic operations, operations are performedin wavelength orders. More specifically, light rays having such awavelength spectrum (wavelengths λ₁ -λ_(m) as shown in FIG. 7(a) areprocessed in the pit 1a, and after they are changed into such awavelength spectrum (with wavelength λ_(a), λ_(b) componentsattenuated), the light rays are divided by the optical interconnection 8between two signal lines, being then caused to become incident again onseparate pits 1b, 1c on the PHB medium 3. The light ray incident on thepit 1b is subjected to separate processing in the pit 1b, and after itis changed to such a wavelength spectrum as shown in FIG. 7(c) (withwavelength λ_(c) component further attenuated), the light ray is causedto become incident again on the optical interconnection 8 again. Thelight incident on the pit 1c is subjected to separate processing in thepit 1c, and after it is changed to such spectral pattern of wavelengthas shown in FIG. 7(d) (with wavelength λ_(d) component furtherattenuated), the light ray is emitted externally. As described above,the gate array in the present embodiment, unlike any conventional gatearray, can execute its gate function in wavelength orders.

FIG. 8 is a schematic diagram showing an embodiment in which the elementof the invention is used as a nonlinear threshold element. Multiplexedwavelength information items are entered from a plurality of pits in thefirst stage CPU into pits 1a, 1b, 1c, in which switching operation asshown in (a) is performed correspondingly to the intensity of incidentlight of each wavelength. More specifically, in the pit 1a a light rayof wavelength λ_(s) only is allowed to transmit, and in the pit 1b, onlya light ray of wavelength λ_(t) is allowed to transmit, no lighttransmission being effected in the pit 1c. As above described, the PHBmedium 3 can function as a wavelength multiplexed nonlinear thresholdelement.

FIG. 9 is a schematic diagram showing an embodiment in which the elementof the invention is used as an optical memory element, such as internalmemory, buffer, and register in an optical computer. Individual elementsused in such a way record wavelength multiplexed optical informationitems having such spectral patterns of wavelengths as shown in FIGS.9(a)-9(c) as they are, in individual pits 1a, 1b, 1c respectively. Withthis embodiment, therefore, information items can be recorded on awavelength multiplexed basis.

FIG. 10 is a schematic diagram showing an embodiment in which theelement of the invention is used as an optical interconnection element.In the drawing, numeral 5 designates an optical interconnection elementand 6 designates a next stage information processing layer for receivinginformation. The optical interconnection element 5 in this embodimenthas a function of controlling the amount of optical transmission with agiven wavelength to a particular pit having the information processinglayer 6 in the case of the global operation among pits. In thisembodiment, therefore, different optical interconnections can be formedwith respect to different wavelengths.

In the foregoing embodiments, pits are of a two dimensional planararrangement. Needless to say, however, the invention is not limited tosuch pit arrangement; the optical computing element can be equallyapplicable in the case where the PHB medium is of a multilayerconfiguration or of a stereoregular and three dimensional structure.

According to the invention, as above described, by using a PHB elementas an optical computing element, it is possible to achieve wavelengthmultiplexing for each pit by the PHB medium in the process of opticalcomputing, thereby to increase the processible volume of information tomore than 1000 times as much as that possible with the prior artarrangement.

Further, in the process of optical computing, it is possible toeliminate the tediousness of arithmetic operation involved insimultaneous parallel information processing and to provide a newoptical computing method which assures high processing efficiency.

The previously referred to FIG. 2 illustrated a pit 1 controlled by acontrol unit 2. Reference is now made to the related FIG. 11 which showsfurther details of the control unit 2 as well as further detailsassociated with the pit 1 for control thereof. FIG. 11 shows, in thisregard, the transparent electrodes 25a and 25b in line with and disposedon opposite sides of the pit 1. There is, thus, a pair of electrodesassociated with each pit. The electrode is a thin transparent film thatis actually formed on both surfaces of the PHB element, as will bedescribed in further detail herein in FIG. 12. Because the PHB elementis electrically insulative, different pairs are only required to bedisposed with proper distance from pair to pair. Respective voltage isapplied to each pair of electrodes.

FIG. 11 illustrates an arrangement for a single pit 1. The signal forvoltage setting is established from the control unit 2. In this regard,note the digital signal for voltage setting at 30. This signal iscoupled to a D to A converter 32 which in turn controls the converter34. The converter applies a voltage to the electrodes 25a and 25b toestablish a predetermined electric field therebetween, which electricfield is a function of the particular voltage set at 30. Thus, thesignal for voltage setting is converted to an analog signal by converter32, and the voltage of the analog signal is changed to a necessary levelfor electrode control by the converter 34.

For a plural number of pits, a plural number of illustrated units areused independently, or PHB medium 3 (See FIG. 5) is shared by a pluralnumber of sets of electrodes which are disposed each separately. Theseparate spacing is also illustrated in FIG. 12 herein.

FIG. 12 shows an example of a multiple pit HPU. The center plate is thePHB medium 3 and the side plates are the electrode plates 26a and 26b.Each of the electrode plates may be constructed of glass, and theassociated transparent electrodes, in other words, plural electrodes 25aand separate plural electrodes 25b, are formed on the surface that facesthe PHB plate.

In FIG. 12, the plates are shown exploded away from each other but inactual practice these plates are disposed in contact. In FIG. 12, thedotted circle areas of the PHB plate represent the pits 1.

The electrodes 25a and 25b are formed in a matrix pattern, and thevoltage application for each electrode is carried on independently oralternatively sequentially. In this regard, it is noted that for thisseparate independent control there are separate pairs of lines 50A, 50Bfrom the plural converters 34 for providing selective and independentcontrol of each of the pair of electrodes associated with a particularpit.

Signals for voltage setting may be provided from a computer forcontrolling the filtering characteristics. The computer would controlthe voltage setting at each of the boxes 30. The number of the controlsignals corresponds to that of the pits and the signals are independentfrom each other so that each pit can be controlled independently. Itwould also be possible to intercouple some of the pairs so that controlcould be gained. However, in FIG. 12, total independent control isillustrated.

FIG. 13 illustrates various diagrams of absorption rate when differentapplied voltages E are applied to a pit. FIG. 13 illustrates that asdifferent voltages are applied, the filtering characteristics (opticalabsorption rate) of the pit change. The optical absorption rate is thereverse of the intensity of the filter passed light. It can be seen thatin FIGS. 13(a), (c) and (d) different wavelengths are being passed.

As this invention may be embodied in several forms without departingfrom the spirit of essential characteristics thereof, the presentembodiment is therefore illustrative and not restrictive, since thescope of the invention is defined by the appended claims rather than bythe description preceding them, and all changes that fall within themeets and bounds of the claims, or equivalence of such meets and boundsthereof are therefore intended to be embraced by the claims.

What is claimed is:
 1. An optical filtering element for use in anoptical computer, comprising:a photo-chemical hole burning elementhaving at least a first pit and a second pit for respectivelytransmitting predetermined wavelength components of light rays eachhaving a plurality of wavelengths incident on the at least first andsecond pits through the photo-chemical hole burning element; and controlmeans for independently controlling a light transmission characteristicof each of the at least first and second pits so that the first pittransmits a first predetermined wavelength component of the light raysand the second pit transmits a second predetermined wavelength componentof the light rays, wherein the first predetermined wavelength componentis different form the second predetermined wavelength component whereinsaid control means includes electrode means for providing an electricfield for each pit.
 2. An optical filtering element as set forth inclaim 1 wherein said electrode means comprises a pair of electrodes, onedisposed on each side of a pit.
 3. An optical filtering element as setforth in claim 1 wherein said control means further includes means forestablishing separate and independent voltages for providing separatecontrol of the electrode means associated with the first and second pitsfor providing different electric fields.
 4. An optical filtering elementas set forth in claim 3 wherein said means for establishing voltagecomprises a digital to analog converter and a DC-to-DC converter.
 5. Anoptical filtering element including a photo-chemical hole burningelement disposed in a substrate having filtering means for selecting atleast one wavelength component from at least one light ray having aplurality of wavelength components incident on the filtering element,means for controlling the filtering means to select wavelengthcomponents including first and second transparent electrodesrespectively disposed on first and second sides of the substrateadjacent to the photo-chemical hole burning element, means forestablishing a digital signal for voltage setting, digital-to-analogconverter means, coupled to the means for establishing, for convertingthe digital signal to an analog signal, DC-to-DC converter means,coupled to the digital-to-analog converter means, for regulating theanalog signal, and means for coupling the DC-to-DC converter means tothe first and second transparent electrodes so that the analog signalsupplied by the DC-to-DC converter means is applied to the first andsecond transparent electrodes to generate an electric field across thephoto-chemical hole burning element such that a wavelength component isselected depending on a voltage applied to the transparent electrodes.6. An optical filtering device including a plurality of photo-chemicalhole burning elements disposed in a substrate, each element havingrespective filtering means for selecting at least one wavelengthcomponent from at least one light ray having a plurality of wavelengthcomponents incident on the filtering device, means for independentlycontrolling the individual filtering means to select wavelengthcomponents including first and second transparent electrodesrespectively disposed on first and second sides of the substrateadjacent to each photo-chemical hole burning element, a plurality ofmeans for respectively establishing a digital signal for voltagesetting, a plurality of digital-to-analog converter means, coupled torespective means for establishing, for respectively converting thedigital signal to an analog signal, a plurality of DC-to-DC convertermeans, coupled to respective digital-to-analog converter means, forrespectively regulating respective analog signals, and a plurality ofmeans, respectively coupling the DC-to-DC converter means to individualsets of first and second transparent electrodes so that the analogsignal supplied by each DC-to-DC converter means is applied to arespective set of first and second transparent electrodes to generate anelectric field across each photo-chemical hole burning element such thata wavelength component is selected depending on a voltage applied to thetransparent electrodes.
 7. An optical filtering element for use in anoptical computer, the optical computer including means for processingcomputing light rays which include a plurality of wavelength componentsfor carrying out computing functions, comprising:a plurality ofindividual photo-chemical hole burning means for selecting at least onewavelength component form the computing light rays; and means forchanging a light transmission characteristic of each photo-chemical holeburning means to select at least one wavelength, wherein said means forchanging a light transmission characteristic comprises a pair ofelectrodes associated with each photo-chemical hole burning means, eachelectrode pair constructed and arranged to effect a change of a lighttransmission characteristic of an individual photo-chemical hole burningmeans.